In the design of an optical system with a gimbaled telescope, for receiving light, transmitting light, or both, with a significant field of regard, there must be an allocation of the optical functions between on-gimbal components and off-gimbal components. The on-gimbal components are pointed as the telescope points, whereas the off-gimbal components are not pointed as the telescope points. If all of the optical components are mounted on the gimbal structure, their large mass and size may require an unacceptably large gimbal structure. Increasing the on-gimbal mass requires the use of a stronger gimbal structure, larger bearings, and larger drive motors. Also, the maximum slew rate of the gimbal is reduced. For some very large and heavy optical components, such as high-power laser transmitters and cryogenically cooled sensor receivers, it is impractical to mount these components on the gimbal. They therefore must be mounted off-gimbal but to the structure to which the gimbal structure is mounted, such as the airframe of an aircraft or the non-gimbaled structure of a spacecraft.
Where at least some of the optical components are mounted off-gimbal, additional optical components must be provided to conduct the beam path between the components mounted on the gimbal and the components mounted off the gimbal. These additional optical components must be geometrically arranged to transmit the beam path continuously as the gimbaled structure is pivoted about the x and y axes.
One such approach is an arrangement of mirrors termed coude optics. The coude optics typically directs the beam path along the axis of rotation of the gimbal axes, to avoid nutation of the beam path about the inner and outer gimbal pivots. Existing approaches to coude optics work well for astronomical applications, where the field of view of the optical system is relatively small. However, a larger field of view and field of regard is normally required for surveillance and other applications. The available coude optics is much less successful for these applications requiring a larger field of view. The result is a tendency to place more of the optical components onto the gimbal structure than would otherwise be desirable from the standpoint of the mechanics of the gimbal structure.
Accordingly, there is a need for an improved approach to communicating the beam path between the on-gimbal and the off-gimbal components, particularly for optical systems requiring a larger field of view and larger field of regard. The present invention fulfills this need, and further provides related advantages.